There are some cases where industrial waste water contains various harmful metal ions. In order to prevent environmental pollution, it is required to sufficiently remove such harmful metal ions from the industrial waste water. On the other hand, many of the harmful metal ions can be effectively used as heavy metals. If, therefore, such harmful metal ions can be separated and collected to be recycled as secondary resources, two advantages of harmful metal ion removal and its recycling are attained simultaneously.
Conventionally, ion-exchange resins have been widely used for removing harmful metal ions or capturing valuable metal ions from industrial waste water. However, conventional ion-exchange resins do not have sufficient ability of selectively adsorbing low metal ion concentration.
Chelating resins also have been used for removing or capturing heavy metals in water treatments. Chelating resins form a chelate with metal ions to selectively capture them. Its ability of capturing metal ions, and especially heavy metal ions, is high. However, many of chelating resins have iminodiaceticacid skeleton introduced therein. This skeleton tends to lower the chelate formation ability of the chelating resins, in particular, the selective adsorption ability thereof at low pH.
Normally, ion-exchange resins and chelating resins are in the form of beads with a rigid three-dimensional structure formed by crosslinking using a cross-linking agent such as divinylbenzene and the like. This structure lowers the diffusion speed of metal ions and regenerants into the ion-exchange resins and the chelating resins and as a result, processing efficiency is lowered. Furthermore, when these resins are of the disposable type which are thrown away after one use without being recycled, it is difficult to burn and dispose them. In this case, there is a problem of how to decrease the volume of the used resins.
In an attempt to solve the problems of the bead-like chelating resins, a fiber-like or sheet-like chelating resin has been proposed (see Japanese Unexamined Patent Publication No. 7-10925). The fiber-like or sheet-like chelating resin has a large specific surface area, and contains on its surface, a chelate functional group which is to be the site of adsorbing and desorbing metal ions. Due to these characteristics, the resin has many advantages, for example, it shows high efficiency of adsorbing and desorbing metal ions, and can be easily burned and disposed. However, there are also disadvantages that the production process thereof is complicated, and the use of an ionizing ray is required in its production. As a result, there are many problems in terms of equipment, safety, and production cost.
The present invention has been achieved in view of the above-described situation, and an objective thereof is to provide a metal chelate forming fiber which can be made by a simple and safe method at low cost, a process for preparing the same, and a metal ion sequestration using the fiber.